Allow Blink to generate cc::FrameSinkId from RenderThread

third_party/WebKit/public/platform/Platform.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 303 matching lines @@
   // Returns the maximum amount of memory a decoded image should be allowed.
   // See comments on ImageDecoder::m_maxDecodedBytes.
   virtual size_t maxDecodedImageBytes() { return noDecodedImageByteLimit; }
 
   // Process -------------------------------------------------------------
 
   // Returns a unique identifier for a process. This may not necessarily be
   // the process's process ID.
   virtual uint32_t getUniqueIdForProcess() { return 0; }
 
+  // Render Thread -------------------------------------------------------
+
+  // Returns a unique client ID for the process of the current render thread
+  virtual uint32_t getClientId() { return 0; }

[Fady Samuel, 2016/11/22 23:41:18]

How about just exposing a "generateFrameSinkId" which is what you really need?

[xlai (Olivia), 2016/11/22 23:51:55]

I would rather keep an interface function as straightforward as possible. 

Another reason, I'm wondering can we directly use cc::FrameSinkId here? WDYT,
kinoku@?

[kinuko, 2016/11/23 10:33:30]

(Putting aside the discussion if it's recommended or not) yes it's possible, a
few public headers actually include cc headers and refer cc types.

+  // Generates a new routing ID. This method normally gets delegated to a
+  // MessageRouter.
+  virtual int generateRoutingId() { return 0; }

[kinuko, 2016/11/23 10:33:30]

Is the 'routing ID' about IPC routing or render thread specific term?  'routing
ID' is not the concept blink usually understands, do we really need this
interface here?

+
   // Message Ports -------------------------------------------------------
 
   // Creates a Message Port Channel pair. This can be called on any thread.
   // The returned objects should only be used on the thread they were created
   // on.
   virtual void createMessageChannel(WebMessagePortChannel** channel1,
                                     WebMessagePortChannel** channel2) {
     *channel1 = 0;
     *channel2 = 0;
   }
@@ skipping 341 matching lines @@
  protected:
   Platform();
   virtual ~Platform() {}
 
   WebThread* m_mainThread;
 };
 
 }  // namespace blink
 
 #endif